This amp I'm looking at buying has a EFX send and a EFX return, which for the most part i hear is for time based effects (Chorus, Flanger etc...). This amp also has a Amp in and a Preamp out. What are these used for?
If you want to use a different preamp, you run that in the "Amp in", and it bypasses your onboard preamp. The "preamp out" is if you want to use your amp only as a preamp, and power the signal with some other method.